The present invention relates generally to rollers for handling moving webs of various materials, and more specifically, to improved low inertia rollers particularly adapted for handling relatively high speed, relatively fragile webs, such as webs of nonwoven materials utilized in the manufacture of disposable diapers and the like.
Manufacturers, whose processes involve web handling, seemingly continually seek higher web processing speeds. Disposable diaper manufacturers are illustrative of such manufacturers since increasing the speed of the webs utilized in making disposable diapers can significantly reduce manufacturing costs on a per diaper basis. The webs used in manufacturing disposable diapers, especially the webs of nonwoven materials, tend to be relatively fragile, and this has often limited the forces that can be exerted in the webs during handling.
In many manufacturing processes involving web handling, webs are introduced into the process from a roll of the web material. Zero-speed splicers are often used to splice the beginning end of the web from a new roll onto the trailing end of an expiring roll. For the zero-speed splicer to work appropriately, the travel speed of the moving web at the splicing point must be brought to zero. After the webs are then spliced together, the web is subsequently accelerated back up to the desired web processing speed.
Rollers are commonly used for the handling and conveyance of web materials, such as webs of nonwoven, plastic, paper, filter and film materials, from one point in a manufacturing process to another. The surfaces of web-handling rollers are usually shaped to a desired profile and are typically required to be rigid. This is because surface imperfections and flexure in web rollers may lead to wrinkles and other imperfections in the web. To maintain the required rigidity and surface requirements, prior web rollers have typically been made from relatively heavy material, such as steel. As a result, such web rollers have a substantial amount of inertia.
To attempt to handle high-rate speed changes with high-inertia rollers, especially in processes including zero speed web splicers, the web handling processes have been required to use extra equipment, including control systems, power supplies and prime movers. This equipment is generally relatively expensive and also requires space on the already crowded, short-of-space manufacturing floor. Also, relatively large amounts of energy must be expended to control the motion of high-inertia rollers.
In addition, such standard web rollers have also required relatively heavy bearings for support. Heavy bearings, in turn, have a substantial amount of friction. The bearing friction continually acts against the acceleration of the web roller. To counteract the bearing friction in standard web rollers, the web handling process requires higher powered equipment and larger amounts of energy than would be required with a low-friction roller.
It has been proposed to convey web material by supporting the web material directly using forced air. For instance, U.S. Pat. No. 5,360,152 describes a cylinder with an outer surface that is perforated with multiple openings to form a bearing or gliding surface for the web material. A disadvantage, however, to supporting the web material directly with air is that many web materials, such as non-wovens, are porous, and supporting a porous web directly with forced air is ineffective. Another disadvantage is that many web processes require the support of flat and rigid roller surfaces to reduce wrinkling and other web imperfections. Air fails to provide the levels of support typically provided by rigid roller surfaces.
Others have suggested using a fluid (including air) to support a web guide roller. U.S. Pat. No. 5,246,155 discloses a roller that includes end seal covers and a support body generally in the shape of a hollow pipe. A thin, cylindrical roller body is carried by and is concentric with the support body. The annular space between the roller body and the support body is filled with a suitable pressure fluid, such as oil. The patent, however, also mentions air as a possible fluid. The pressure fluid is introduced into annular space by a plurality of equi-radially spaced and disposed feed lines, and is withdrawn from the annular space primarily through deflector channels disposed at the ends of the support body. Although the patent states of that the roller body is allowed to rotate with respect to the roller support body in an essentially frictionless manner, this statement must be questioned. With the pressure fluid exerting the same pressure throughout the annular space on the roller body the force exerted by the web, as it passes about a portion of the roller body, would cause the portion of the roller body to be moved into friction contact with adjacent portion of the roller support body. Such contact may be said to be essentially frictionless in the context of a printing press employing a paper web, and particularly when oil is the pressure fluid. However, if air were to be employed, the frictional contact would render the patented web guide roller unusable, particularly if attempts were made to use the patented web guide roller to handle relatively high speed, relatively fragile webs, such as used in the manufacture of disposable diapers.
Those working in the art of handling relatively high speed, relatively fragile webs have long recognized that a need existed for an improved web-handling roller that has low inertia and low friction and that is capable of providing rigid support for such webs.
An object of the present invention is to provide a web-handling roller that has relatively low inertia and relatively low friction and that may be used in handling relatively high speed, relatively fragile webs, such as the webs utilized in the manufacture of disposable diapers and the like. A further object of the present invention is to provide a low inertia, web-handling roller that provides rigid web support for such webs.
The foregoing objects are met in whole or in part by the present invention that provides an improved low inertia roller adapted for handling relatively high speed, relatively fragile webs, such as webs utilized in the manufacture of disposable diapers and the like. The improved roller includes a relatively fixed, inner tube. This inner tube has a radially outwardly facing surface, first and second ends, and a longitudinal central axis. A web contacting outer tube, which also has first and second ends, and a longitudinal central axis, is disposed about the inner tube so that the longitudinal central axes of the inner and outer tubes are coaxial and so that the outer tube may rotate about the coaxial central axes with respect to the inner tube, with minimal friction therebetween. The outer tube has radially outwardly facing and radially inwardly facing surfaces. The inwardly facing surface of the outer tube and the outwardly facing surface of the inner tube define an annular gap or space therebetween that has a preselected radial thickness or dimension. The annular gap has a first, partially circumferentially extending portion, adjacent the partially circumferentially extending portion of the outer tube, which is adapted to be in contact with a web as the web passes about the roller. The annular gap also has a second, partially circumferentially extending portion spaced circumferentially from the first portion. Longitudinally extending grooves in the inner tube are adjacent the first and second portions and may constitute parts of the portions. The inner tube has a first fluid passage that is in fluid communication with a source of pressurized compressible fluid. A second fluid passage in the inner tube is adapted to exhaust compressible fluid from the inner tube, and is in fluid communication with the second portion of the annular gap. A fluid flow restriction device in the inner tube includes a restricted fluid flow path that permits the flow of compressible fluid, in a preselectedly restricted manner, from the first passage to the first portion of the annular gap. The radial dimension of the annual gap, between the first and second portions, is selected so that there is a reduction in the pressure of the compressible fluid as the fluid passes from the first portion of the annular gap to the second portion of the annular gap and so that the force of the web passing around the outer tube is substantially balanced by the pressure of the compressible fluid in the first portion of the annular gap.
In addition to the low inertia and relatively low friction running, the improved roller of the present invention includes what can be described as a xe2x80x9cfeedback systemxe2x80x9d feature. Due to the functioning of the air gap, which causes a difference (decrease) in the fluid pressures between the first and second portions of the air gap, the force that is exerted by a web on the outer tube is always countered by the force exerted by the fluid in the first portion of the annular gap.